In QGIS 3.10, the data for the layer SIMnodes seem to be OK as inspected in the respective data table but trying to save it into a shapefile:
cSIMnodes = QgsProject.instance().homePath() + '\\SIMnodes.shp'
QgsVectorFileWriter.writeAsVectorFormat(layer = SIMnodes,
fileName = cSIMnodes,
fileEncoding = 'UTF-8',
destCRS = QgsCoordinateReferenceSystem(4326),
driverName = 'ESRI Shapefile')
yields all real numbers in the resulting Esri shapefile to be wrong {for example 234.5 is written as 2.0}.
All integers and all strings are written well.